Songbirds are among the very few organisms that, besides humans, evolved vocal learning, and their study has helped uncover the neuronal basis of vocal communication and vocal learning. To learn to produce their own song and to perform social behaviors requiring individual recognition, songbirds need to process and to form long-lasting memories of the songs they hear in life. While there has been much progress with regards to motor aspects of birdsong, our understanding of the brain areas and mechanisms used by songbirds to analyze and store song auditory information is still very limited. Significant insight into auditory and perceptual aspects of birdsong has derived from the finding that a marked induction of the zenk gene occurs in the caudomedial neostriatum (NCM) when birds hear song. zenk encodes a transcriptional regulator linked to neuronal plasticity, and NCM is part of the central auditory pathway of the songbird brain. Evidence from molecular, anatomical, electrophysiological, and behavioral studies indicate that NCM plays a major role in song auditory processing. In particular, evidence has been uncovered for an auditory representation of song syllables in NCM. These studies also suggest that zenk induction by song in NCM represents an early event in a gene regulatory cascade that leads to long-lasting neuronal changes and possibly the formation and/or storage of song auditory memories. The objective of the proposed research is to characterize the functional and anatomical organization of NCM, and to determine the role of the genomic response to song that occurs in NCM. The specific aims are: 1) to identify stimulus parameters that are critical determinants of the NCM response to song and to determine whether the syllabic representation in NCM is innate or dependent on experience; 2) to determine the anatomical organization of NCM by using small injections of neuronal tract-tracers to examine the extent to which functional sub-domains within NCM have distinct connectivities; and 3) to determine the role of song-induced expression in NCM by a) identifying song regulated zenk target genes in NCM, and b) determining the role of zenk in the long-term habituation of NCM neurons to song. The outcomes of the proposed research will provide basic insights into how the brains of vertebrates process and store behaviorally relevant auditory information, which will eventually help us understand brain mechanisms associated with speech and language disorders in humans.